Bicycle driving mechanism.



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NiTEeD STATES THOMAS C. ROBINSON, OE REvERE, MASSACHUSETTS, ASSICNOE OEONE- HALE To E. BAKER WELCH, OE CAMBRIDGE, MASSACHUSETTS.

BICYCLE DRIVING MECHANISIVI.

SPECIFICATION forming part of Letters Patent No. 641,729, dated January23, 1900.

Application lecl November l2, 1898. Serial No. 696,210. (No model.)

T0 @ZZ whom it may concern: v

Be it known that I, THOMAS C. ROBINSON, of Revere, in the county ofSuffolk and State of Massachusetts, have invented certain new and usefulImprovements in Bicycle Driving Mechanism, of which the followingis aspecification.

` This invention relates to driving mechanisms for bicycles and othervehicles of the kind which employs eccentrics for controlling thecrankmechanism whereby the length of the cranks varies in different portionsof the stroke, being -longer on the downstroke, where most of the riderspower is available, than on the upstroke.

The invention has for its object to improve the connections between thecranks and the crank-axle.

With this obj ect in View the invention consists in the improvementswhich l shall now proceed to describe and claim.

Of the accompanying drawings, forming a part of this specification,Figure 1 represents a side elevation of a bicycle driving mechanismconstructed in accordance with my invention. Fig. 2 represents a frontelevation thereof. Fig. 3 represents a section on line 3 3 of Fig. 1.Fig. 4 represents a section on linee 4 of Fig. 3. Fig. 5 represents asection on line 5 5 of Fig. 3. Fig. 6 represents an enlarged detailsection of the eccentric, showing the manner of attaching it to theframe. Fig. 7 represents a detail section of the eccentricstrap, showingthe provisions for taking up the wear. Fig. 8 represents a perspectiveview of one of the dust-caps employed.

The same reference characters indicate the same parts in all theiigures.

Referring to the drawings, a a a2 designate the frame-bars of abicycle-frame ofthe ordinary diamond type, althoughnit will beunderstood that my invention is equally applicable to drop-frames andframes of other construction.

b designates the rear wheel, 'c the forward sprocket-wheel, keyed orotherwise suitably secured to the crank-axle in the usual manner, and c'the driving-chain.

c4 and a5 are lugs integrally formed on the bicycle-frame and aording ameans for attaching the eccentrics. The lower lug a4,

which projects forwardly and downwardly to a point beyond the rim ofthe'sprocket-wheel c, is preferably attached to the barrel orcrank-hanger a3 of the frame, an additional lug being forged on saidbarrel for the attachment of said lug or projection a4. The latterconsists of a piece of tapered tube brazed to the said additional lugand carrying at its end a tubular cross-piece a6, the end of the tube a4being lap-brazed around saidcrosspiece. The lug or projection a5 on theframebar a is lap-brazed around said bar a, and a tubular cross-piece a7is attached to it in a similar manner to the cross-bar a6.

Two eccentrics are attached to thebicycleframe, one On either side, inthe position represented in Fig. 1. Each eccentric consists ,of a fixedportion d and a strap d', between which are interposed a series ofantifrictionballs d5 d5, twelve being shown in the drawings and heldapart by means of a separator d, consisting of a ring perforated for thereception of the balls. The fixed portiond of the eccentric consists ofa rim having integral ears d2 d3 d4 for attachment to the bicycleframe.The ears d2 and cl3 are attached-to the cross-pieces a6 0.7 at the endsof the projections a4 a5 by means of through-bolts e e', said ears beingslightly recessed, as shown in Fig. 6, to receive the end of the tubularcrosspiece. The third ear d4 on the sprocket side of the machine islonger than the other two ears, extending rearwardly-past the rim of thesprocket c and being attached to the rear fork d2 by means of a screwe2. Said fork or bar a2 is preferably reinforced on the inside at thepoint where the screw e2 enters. On the opposite side of the machinefrom the sprocket the ear corresponding to the ear d4 (shown in Fig. 1)is somewhat shorter. This method of afxing the eccentrics to abicycleframe affords great rigidity, and hence a smooth working of thecrank mechanism, which is essential in a device of this kind, while atthe same time aifording a light construction and permitting theeccentric to be easily removed and positioned.

The strap d instead of being constructed in two halves in the usualmanner is made in a single piece or ring split transversely and formedat its ends with lugs d? d8, hav- IOO ing holes for the reception ofsecuring-bolts dD di. The lug d? is apertured at CU2 for the receptionofthe pivot-bltf2, which forms the connection between the crank fand theeccentric-strap d. Then the mechanism is rst assembled, one or more thinmetal strips or shims d d10 may be inserted between the lugs C17 d8, andas wear occurs in the ball-race these shims are taken out t0 maintain atight adjustment. To exclude dust, the iixed part (l of the eccentricand the strap dl are formed on their opposite edges with short flangesZ13 (ZM. The ends of the crank-axle are provided with bearing-boxesthrough which the cranks ff are permitted t0 slide, so that when poweris applied to the pedals f f the cranks will revolve the axle in theusual manner; but by reason of their connection at f2 f2 with theeccentric-straps said cranks will be constrained to revolve in a circlewhose center is the center of the eccentric, and the pedal willtherefore be farther away from the crankaxle on the downstroke andnearer to said crank-axle on the upstroke, thus giving a greaterleverage on the downstrol-:e and employing to the best advantage theriders power. Said bearing-boxes at the ends of the axle are constructedas follows: In the present instance said axle is shown in two parts orsleeves g g, formed to interlock at their inner ends and held togetherby means of a bolt g. The usual antifriction-bearings g'*Z are providedfor said axle. Each sleeve gis enlarged at its end to form a head orblock g3, which is centrally recessed to re ceive the crankf. It willbeunderstood that these end bearing-blocks would be made separate in thecase of a solid axle and keyed thereto in a suitable manner. In therecesses of each bearing-block, between said block the crank, areinterposed two hardened bearing plates or gibs g5 g5 to receive the wearof the antifriction-balls gA1 g4, of which two endless rows areprovided, one on either side of the crank, said cranks being preferablyhardened and grooved on either side at f3 f3. The gibs g5 are providedwith apertures gw g1g in their ends, through which the balls pass fromthe crank-grooves, while the block g3 is grooved on the outside lnovalor the substitution of new for worn ones. In recesses in the ends ofeach gib g5 are placed small plungers Q13 g13,of felt,which project intothe grooves f3 in the cranks and serve to exclude dust from the ballsgm. Behind the plungers are placed light springs g1'l g, which presssaid plungers against the cranks. Then wear occurs in the bearingblock,the hardened plates or gibs g5 may be set out by interposing thin metalshims be tween said gibs and the blocks g3.

I do not herein claim a compensating connection between the pedal andthe crank, said connect-ion located on the opposite side of the centerof the pedal path from the pedal, since the said subject-matter isclaimed in a copending application filedl by me Decem-berv 2G, 1899,sei-m1 No. 741,587.

I claim- In a bicycle driving mechanism, the combination of thebicycle-frame, an eccentric affixed thereto, the crank-axle having therecessed bearing-blocks at its ends, cranks operating in said blocks andattached to the eccentric-straps, the hardened bearing-gibs g5 occupyingthe recesses in said bearing-blocks, the antifriction-balls interposedbetween said gibs and the cranks, the dust-cap g covering thebearing-block and holding the gibs g5 in place therein, and the screwssecuring said dust-cap to the bearing-block.

In testimony whereof I have affixed my signature in presence of twowitnesses.

O. F. BROWN, A. D. HARRISON.

